[cmake] Declare LLVM_CMAKE_PATH for use in subprojects

[mgorny]

Summary

Declare the LLVM_CMAKE_PATH to the source directory location of CMake
files, in order to make it possible to easily use them in subprojects.
Such a variable is already declared in most of LLVM projects
(and inconsistently mixed with direct source tree references), including
Clang, LLDB, compiler-rt, libcxx... Declaring it inside main LLVM tree
makes it possible to avoid having to declare fallback values or use
conditionals in those projects.

It should be noted that in some of the subprojects LLVM_CMAKE_PATH is
used to reference generated LLVMConfig.cmake file. However, these
references are conditional to stand-alone builds and explicitly
including this file is unnecessary in combined builds.

[mgorny]

Please let me know if I should post related patches to other projects for review, or just commit them? Assuming they're pretty much about changing get_svn_script alike in LLVM.

[beanz]

LGTM. Feel free to commit the patches for other projects too. Thanks!

[mgorny]

Thanks. Committed now, and updates for other projects will follow shortly.

CMakeLists.txt

 
 # Each of them corresponds to llvm-config's.
 set(LLVM_TOOLS_BINARY_DIR ${LLVM_RUNTIME_OUTPUT_INTDIR}) # --bindir
 set(LLVM_LIBRARY_DIR      ${LLVM_LIBRARY_OUTPUT_INTDIR}) # --libdir
 set(LLVM_MAIN_SRC_DIR     ${CMAKE_CURRENT_SOURCE_DIR}  ) # --src-root
 set(LLVM_MAIN_INCLUDE_DIR ${LLVM_MAIN_SRC_DIR}/include ) # --includedir
 set(LLVM_BINARY_DIR       ${CMAKE_CURRENT_BINARY_DIR}  ) # --prefix
 
+# Note: LLVM_CMAKE_PATH does not include generated files
+set(LLVM_CMAKE_PATH ${LLVM_MAIN_SRC_DIR}/cmake/modules)
 set(LLVM_EXAMPLES_BINARY_DIR ${LLVM_BINARY_DIR}/examples)
 set(LLVM_INCLUDE_DIR ${CMAKE_CURRENT_BINARY_DIR}/include)
 
 set(LLVM_ALL_TARGETS
   AArch64
   AMDGPU
   ARM
   BPF

lib/LTO/CMakeLists.txt

find_first_existing_file(${out_var}
     )
 endmacro()
 
 find_first_existing_vc_file(llvm_vc "${LLVM_MAIN_SRC_DIR}")
 
 # The VC revision include that we want to generate.
 set(version_inc "${CMAKE_CURRENT_BINARY_DIR}/LLVMLTORevision.h")
 
-set(get_svn_script "${LLVM_MAIN_SRC_DIR}/cmake/modules/GenerateVersionFromCVS.cmake")
+set(get_svn_script "${LLVM_CMAKE_PATH}/GenerateVersionFromCVS.cmake")
 
 if(DEFINED llvm_vc)
   # Create custom target to generate the VC revision include.
   add_custom_command(OUTPUT "${version_inc}"
     DEPENDS "${llvm_vc}" "${get_svn_script}"
     COMMAND
     ${CMAKE_COMMAND} "-DSOURCE_DIR=${LLVM_MAIN_SRC_DIR}"
                      "-DNAME=LLVM_REVISION"